The author made a tour in North Wales, having two objects principally in view: the first, to classify the stratified rocks of that country; the second, to ascertain what are the beds that lie below the Silurian rocks of Sir R. Murchison, and whether those beds contain any organic remains. After first observing the structure of those parts of the country where the order of superposition in the beds was already known, he proceeded to examine other districts where the arrangement of the rocks is more obscure and complicated. Upper Silurian Rocks.—Llangollen district He began by studying the Llangollen district, described by the late Mr. Brown. He agrees that geologist in referring the Upper Silurian rocks in that neighbourhood, partly to the Ludlow and partly to the Wenlock series of Sir R. Murchison. Ludlow series. — This series, in descending order, consists of 1. Thin, grey, micaceous beds, containing Terebratula navicula, Leptæna lata, several species of Cypricardia, and other fossils 2. Liver-coloured shales. 3. Blue shale The distinction which exists in the English border countries, between the Upper and Lower Ludlow beds, cannot her be made out; nor is there any trace of the Aymestry limestrone. There are so few fossils in the greater part of the Ludlow amd Wenlock series in North Wales, that it is by differences of colour or minieral composition that one is often obliged to distinguish them. The Ludlow series is of soft texture, is